The invention relates to a colour display tube comprising an envelope having a substantially rectangular display window provided with an upright edge and a substantially rectangular colour selection electrode having a large number of apertures, which electrode is suspended in the corners of the display window by means of a strip-shaped resilient element connected to each corner of the colour selection electrode, which resilient element is substantially perpendicular to the direction of electron beams deflected towards the relevant corner of the display window, and which resilient element has a peg at its end remote from the colour selection electrode.
Such a colour display tube is disclosed in Netherlands Patent Application No. 6701 585 to which British Pat. No. 1,189,403 corresponds. The strip-shaped resilient elements connected to the corners of the colour selection electrode ensure that in the case of expansion the colour selection electrode moves towards the display window. The strip-shaped resilient elements have a peg at their end remote from the colour selection electrode. Conical holes are drilled in the corner of the upright edge of the display window. The colour selection electrode is suspended in the display window by placing the pegs in the conical holes.
However, in order to obtain a good resistance to shocks, it is necessary for the resilient elements in such a tube to exert a large pressure on the holes in the edge of the display window, since otherwise the pegs work loose from the holes. In colour selection electrodes which do not comprise a rigid carrier frame, however, this results in deformations of the colour selection electrode at the usual temperature treatment to which the tubes are subjected during the manufacture. Moreover, the drilling of holes in the upright edge of the display window gives an increased possibility of fracture during the manufacture of the tube.
It therefore an object of the invention to provide a suspension of a colour selection electrode in a colour display tube which has a large resistance to shocks.
Another object of the invention is to provide a suspension of a colour selection electrode in a display tube with which possibility of fracture of the tube is considerably reduced.
A further object of the invention is to provide a suspension of an internal conical screening cap which is adapted to the suspension of the colour selection electrode.
According to the invention, a colour display tube of a kind mentioned in the opening paragraph is characterized in that the axis of the peg extends substantially parallel to the direction of the electron beams directed towards the relevant corner, which peg comprises a conical portion, and that in the corner of the upright edge of the display window a supporting element is connected, which supporting element comprises a portion extending perpendicularly to the axis of the peg, which portion comprises an aperture and through which aperture the conical portion of the peg falls partly. Since the axis of the peg is perpendicular to the resilient element and the supporting element comprises a portion extending perpendicularly to the axis, the peg always extends equally far through the aperture in the supporting element. The resilient elements only exert a very small pressure on the supporting elements. As a result of the position of the peg and the portion of the supporting element with the aperture, the colour selection electrode can be dis-assembled and assembled again in a simple manner. The aperture in the supporting element is preferably a triangular aperture. Herewith it is achieved that the conical portion of the peg engages the edges of the aperture in a reproducible manner.
A further embodiment is characterized in that at its end remote from the strip-shaped resilient element the peg has a locking hook extending towards the colour selection electrode. In the case of shocks perpendicular to the display window in a direction away from the display window, the peg locks itself in the aperture of the supporting element. When shocks occur perpendicularly to the display window in a direction towards the display window, the forces on the peg are such that the peg works loose from the aperture. In order to prevent the colour selection electrode from working loose when such shocks occur, the peg comprises a locking hook which extends towards the colour selection electrode.
Still a further embodiment is characterized in that for at least one strip-shaped resilient element the peg forms part of a metal plate which is connected to the end of the strip-shaped resilient element remote from the colour selection electrode. In order to ensure that the colour selection electrode is not deformed in the assembled condition, the position of the pegs should correspond accurately to the position of the apertures in the supporting elements. In principle, three resilient elements can directly be provided with a peg and be placed with the pegs in the relevant apertures in the supporting elements. As a result of this the position of the fourth peg is fixed. By means of a separate metal plate comprising a peg the position of the fourth peg is adapted to the position of the aperture in the fourth supporting element. Plates provided with a peg are preferably secured to three or four resilient elements. Herewith it is effected that each time two resilient elements situated at a diagonal opposite to each other engage with the pegs the edges of the apertures in the supporting element at the same clamping pressure.
Again a further embodiment is characterized in that the supporting element has at least one projection, which projection is sealed in the upright edge of the display window. The projections are sealed in the upright edge of the display window at right angles or obliquely whether or not provided already with the portion of the supporting element which extends substantially perpendicularly to the axis of the peg.
A further favourable embodiment is characterized in that the projection is constructed as a hollow sleeve the diameter of which, taken from the bottom of the sleeve, increase stepwise and which sleeve is sealed in the upright edge with its part having the smaller diameter. The sleeve is sealed in the upright edge by directing a gas flame to the bottom of the sleeve so that the sleeve sags into the glass. Since the gas-flame does not touch the glass surface of the upright edge, the glass surface during sealing remains smooth. This is of importance when during providing the luminescent phosphors on the display window the excess of phosphor suspension is poured out.
According to another embodiment the supporting element is cemented to the upright edge of the display window.
Again another embodiment is characterized in that the tube has a conical internal screening cap, which screening cap comprises a suspension element in each corner, which suspension element is connected to the supporting element connected in the upright edge of the display window. Usually an internal conical screening cap is used in display tube so as to screen the electron beams from the earth's magnetic field. The internal screening cap should be connected so that movements of the screening cap are not transferred to the resilient elements with which the colour selection electrode is suspended. This is effected by suspending the screening cap from the supporting element which is fixedly connected in the upright edge of the display window.
A further other embodiment is characterized in that the suspension element comprises a portion extending parallel to the strip-shaped resilient element, which portion extends at a distance smaller than the thickness of the peg of the strip-shaped resilient element. As a result of this it is prevented that the pegs work loose from the apertures in the supporting elements without it being necessary for the peg itself to comprise a locking hook.
Still a further other embodiment is characterized in that the suspension element comprises an aperture and that the strip-shaped resilient element at its end remote from the colour selection electrode has a pin which extends substantially parallel to the upright edge of the display window, said pin extending through the aperture in the suspension element. The pin which can make a small stroke in the aperture of the suspension element in the corner of the screening cap prevents the pegs from working loose from the apertures in the supporting elements in the case of shocks of the display tube.